Internal combustion engines generally require a breather system to take gas, which escapes from the cylinders into the crankcase region, up through the cylinder block and head and out through the cover from where they are fed back into the air intake system for the cylinders. The breather gases generally pass up through oil drainage passages in the engine. In engines with overhead camshafts they therefore pass around the cam shaft, which tends to result in significant amounts of oil being carried out with the breather gases which increases the unwanted emissions from the engine.
Various developments have been made to overcome this problem by separating the region in the cylinder head through which gases flow from the camshaft, as shown, for example, in GB 2 125 482. However the present invention aims to provide a simpler and more effective solution to the problem.